t 389 ] 
peated, and with neaiiy,the fame fuccefs, with another 
moufe, and another quantity of this air, the virtue of 
which had been impaired. Examining all the degrees 
of the calcination of lead, I found nothing but fixed air, 
or a little phlogijiicated common air, till I came to majli- 
cot, which is a ifate that precedes the red lead. This gave 
air about twice as good as common air, and the litharge, 
which follow’s the red lead, ga^e fixed again. Pmman 
vitriol and fedative fait yielded air which was, as nearly 
as. pOlfible, of the fame degree of purity with common 
air. My conjedtures concerning the caufe of thefe ap- 
pearances are as yet too crude to lay before the Society. 
My prefent ideas of the lafi: mentioned fadts are, that, 
together with other obfervations which I Ihall lay before 
the publick, they afford fome foundation for fuppofing^ 
that the nitrous wcid is the balls of common air, and that 
nitre is formed by a decornpofition of the atmofphere. 
But it is poffible I may think otherwife to-morrow, h ^ 
is happy, when with a fertility of invention fufficient to 
raife hypothefes, a perfon is not apt to • acquire ^too great 
attachment to them. By this means they lead to the dif- 
covery of new fadts:, and from a fufficient number ©f 
thefe the true theory of nature will eafily refult. 
I have made many other original experiments oEa 
mifcellaneous natufe; but I fhall not take up your time 
W ith the mention of them in this place. If this imper- 
fedt communication gives you, or the Society, any fatif- 
-fddtion, I flaall be very happy, and fhall be encouraged to 
profecute 
• i ‘j 
